docs: def from_fields(cls, **kwargs):
          '''
          Create an `Atom` instance from a set of fields. This is a
          slightly faster way to initialize an Atom.
          
          **Example**
  
          >>> Atom.from_fields(type='Ar',
                               r_array=np.array([0.0, 0.0, 0.0]),
                               mass=39.948,
                               export={})
          '''
          obj = cls.__new__(cls)
          
          for name, field in obj.__fields__.items():
              if name in kwargs:
                  field.value = kwargs[name]
          
          return obj